Block, D. L. and Combes, F. and Puerari, I. and Freeman, K. C. and Stockton, A. and Canalizo, G. and Jarrett, T. H. and Groess, R. and Worthey, G. and Gehrz, R. D. and Woodward, C. E. and Polomski, E. F. and Fazio, G. G. (2007) Keck spectroscopy and Spitzer space telescope analysis of the outer disk of the Triangulum spiral galaxy M 33. Astronomy and Astrophysics, 471 (2). pp. 467-474. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20091028-082750601
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In an earlier study of the spiral galaxy M 33, we photometrically identified arcs or outer spiral arms of intermediate age (0.6-2 Gyr) carbon stars precisely at the commencement of the HI-warp. Stars in the arcs were unresolved, but were likely thermally-pulsing asymptotic giant branch carbon stars. Here we present Keck I spectroscopy of seven intrinsically bright and red target stars in the outer, northern arc in M 33. The target stars have estimated visual magnitudes as faint as V~25^(m). Absorption bands of CN are seen in all seven spectra reported here, confirming their carbon star status. In addition, we present Keck II spectra of a small area 0.5 degree away from the centre of M 33; the target stars there are also identified as carbon stars. We also study the non-stellar PAH dust morphology of M 33 secured using IRAC on board the Spitzer Space Telescope. The Spitzer 8 µm image attests to a change of spiral phase at the start of the HI warp. The Keck spectra confirm that carbon stars may safely be identified on the basis of their red J-K_s colours in the outer, low metallicity disk of M 33. We propose that the enhanced number of carbon stars in the outer arms are an indicator of recent star formation, fueled by gas accretion from the HI-warp reservoir.
|Additional Information:||© ESO 2007. Received 26 June 2006. Accepted 15 May 2007. This paper was completed whilst DLB was a Visiting Professor at the Mount Stromlo and Siding Spring Observatories, Canberra; the hospitality of Ken and Margaret Freeman is very warmly acknowledged. D.L.B. and I.P. are indebted to the Anglo American Chairman’s Fund, Mr. C. Sunter, Mrs. M. Keeton and the Board of Trustees. I.P. acknowledges support from the Mexican foundation CONACyT under project 35947–E. This paper is based in part on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the financial support of the W. M. Keck Foundation. This work is also partially based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. R.D.G. and C.E.W. were supported by NASA through an award issued by JPL/Caltech. D.L.B. warmly thanks the Vice-Chancellor of the University of the Witwatersrand for the Vice-Chancellor’s Research Award in 2006. D.L.B. also expresses much gratitude to Fani Titi of the TISO Foundation for his stellar support. We thank M. Ashby, P. Wood and S.P. Willner for their input. Finally, we thank the anonymous referee for insightful comments.|
|Subject Keywords:||galaxies : evolution; galaxies : spiral; galaxies : individual : M33 (NGC598); galaxies : Local Group; galaxies : formation; galaxies : stellar content|
|Official Citation:||Keck spectroscopy and Spitzer space telescope analysis of the outer disk of the Triangulum spiral galaxy M 33 D. L. Block, F. Combes, I. Puerari, K. C. Freeman, A. Stockton, G. Canalizo, T. H. Jarrett, R. Groess, G. Worthey, R. D. Gehrz, C. E. Woodward, E. F. Polomski and G. G. Fazio A&A 471 (2) 467-474 (2007) DOI: 10.1051/0004-6361:20065908|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||30 Oct 2009 17:32|
|Last Modified:||26 Dec 2012 11:30|
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